Apparatus and method for allocating channel state information-reference signal in wireless communication system

ABSTRACT

Embodiments of the present invention relate to a wireless communication system, and more particularly, to a technology for allocating a Channel State Information-Reference Signal (CSI-RS) in a wireless communication system. Embodiments of the present invention provides an apparatus and method for allocating CSI-RSs to resource areas, in which, under the condition of a subframe in which the CP is an extended CP, and the duplex scheme is TDD, if CSI-RSs for maximum 8 antenna ports are allocated, the CSI-RSs are allocated to the 8th and 9th symbols (symbol No. l=7 and 8), wherein each CSI-RS for every two antenna ports is allocated to the same RE while being discriminated from each other by an orthogonal code and neighbor CSI-RS allocated REs in the frequency axis are spaced by an interval of three REs.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/299,679, filed on Jun. 9, 2014, which is a continuation of U.S.patent application Ser. No. 13/149,225, filed on May 31, 2011, all ofwhich claims priority from and the benefit under 35 U.S.C. §119(a) ofKorean Patent Application No. 10-2010-0052033 filed on Jun. 1, 2010 andKorean Patent Application No. 10-2010-0055073 filed on Jun. 10, 2010,which are hereby incorporated by reference for all purposes as if fullyset forth herein.

BACKGROUND

1. Field

Embodiments of the present invention relate to a wireless communicationsystem, and more particularly, to a technology for allocating a ChannelState Information-Reference Signal (CSI-RS) in a wireless communicationsystem.

2. Discussion of the Background

With the development of communication systems, a wide variety ofwireless terminals are being used by consumers, such as businesscompanies and individuals.

Mobile communication systems, such as 3GPP (3rd Generation PartnershipProject) including LTE (Long Term Evolution) and LTE-A (LTE Advanced),allow for the development of technology for a high-speed large-capacitycommunication system, which can transmit or receive various data, suchas images and wireless data, beyond the capability of providing a voiceservice, and can transmit data of such a large capacity as thattransmitted in a wired communication network. Moreover, the currentmobile communication systems are requiring a proper error detectionscheme, which has a goal to minimize the reduction of information lossand improve the system transmission efficiency, thereby improving thesystem performance.

Further, in various current communication systems, various ReferenceSignals (RSs) are used in order to provide information of acommunication environment, etc. to a counterpart device through anuplink or a downlink.

For example, in a Long Term Evolution (LTE) system, which is an evolvedsystem for mobile communication, a Cell-specific Reference Signal (CRS)is transmitted as a reference signal at each sub-frame in order toobtain channel information in the downlink transmission.

At this time, since the maximum number of antennas supportable in thedownlink of the LTE system is four, different CRSs are allocated to andtransmitted through a maximum of four antenna ports according to thetime/frequency.

The next generation communication technologies, such as the LTE-A, cansupport eight antennas in the downlink. Therefore, the current CRSsdefined for four existing antennas are insufficient for detection ofchannel information at the time of downlink transmission. In order toovercome such a problem, a reference signal named “Channel StateInformation-Reference Signal (CSI-RS)” has been newly defined to obtainchannel state information of a maximum of eight antennas.

In other words, a communication system using a maximum of eight MultipleInput Multiple Output (MIMO) antennas at both the transmission port andthe reception port may be used, and a scheme of transmitting CSI-RSs,UEs of which are different according to the antenna ports or antennalayers for the transmission or reception of the signals, may also beused. Presently, only basic definitions for the CSI-RS and definitionsfor the resource overhead have been arranged. However, methods forallocating corresponding CSI-RS patterns to resource areas by eachantenna port in each eNB (or eNodeB) or cell have not been specificallyarranged yet.

Especially, the length of the Cyclic Prefix (CP), Duplex scheme, etc.may change the form or type of the subframe to which the CSI-RSs will beallocated. However, there has been no discussion about a scheme forallocating CSI-RSs to each antenna port in such a case.

SUMMARY

Additional features of the invention will be set forth in thedescription which follows, and in part will be apparent from thedescription, or may be learned by practice of the invention.

An exemplary embodiment of the present invention discloses an apparatusor a method for allocating Channel State Information-Reference Signals(CSI-RSs) for maximum 8 antenna ports to resource areas including aplurality of Resource Elements (REs), under a condition of a subframe inwhich an extended Cyclic Prefix (CP) is employed as a CP, a TimeDivision Duplex (TDD) scheme is employed as a duplex scheme, wherein theCSI-RSs are allocated to 8th and 9th symbols (symbol number l=7 and 8),each CSI-RS for every two antenna ports is allocated to an identical REwhile being discriminated from each other by an orthogonal code, andneighbor CSI-RS allocated REs in the frequency axis are spaced by aninterval of three REs. The other exemplary embodiment of the presentinvention discloses an apparatus for receiving Channel StateInformation-Reference Signals (CSI-RSs), the apparatus comprising: asignal receiver for receiving an Orthogonal Frequency DivisionMultiplexing (OFDM) signal, which is generated through allocation ofCSI-RSs for maximum 8 antenna ports, under a condition of a subframe inwhich an extended Cyclic Prefix (CP) is employed as a CP, a TimeDivision Duplex (TDD) scheme is employed as a duplex scheme; a CSI-RSextractor for extracting CSI-RSs for each of the multiple antenna portsallocated to particular REs from a signal received by the signalreceiver; and a channel state measurer for acquiring Channel StateInformation (CSI) based on the extracted CSI-RSs, wherein the CSI-RSsare allocated to 8th and 9th symbols (symbol number l=7 and 8) when theCSI-RSs are allocated to maximum 8 antenna ports, each CSI-RS for everytwo antenna ports is allocated to an identical RE while beingdiscriminated from each other by an orthogonal code, and neighbor CSI-RSallocated REs in the frequency axis are spaced by an interval of threeREs.

The other exemplary embodiment of the present invention discloses amethod for receiving Channel State Information-Reference Signals(CSI-RSs), the method comprising the steps of: receiving an OrthogonalFrequency Division Multiplexing (OFDM) signal, which is generatedthrough allocation of CSI-RSs for maximum 8 antenna ports, under acondition of a subframe in which an extended Cyclic Prefix (CP) isemployed as a CP, a Time Division Duplex (TDD) scheme is employed as aduplex scheme; extracting CSI-RSs for each of the multiple antenna portsallocated to particular REs from the received signal; and acquiringChannel State Information (CSI) based on the extracted CSI-RSs, whereinthe CSI-RSs are allocated to 8th and 9th symbols (symbol number l=7 and8) when the CSI-RSs are allocated to maximum 8 antenna ports, eachCSI-RS for every two antenna ports is allocated to an identical RE whilebeing discriminated from each other by an orthogonal code, and neighborCSI-RS allocated REs in the frequency axis are spaced by an interval ofthree REs.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and areintended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention, andtogether with the description serve to explain the principles of theinvention.

FIG. 1 is a block diagram illustrating a structure of a CSI-RSallocation apparatus according to an exemplary embodiment of the presentinvention.

FIGS. 2 to 14 illustrate various CSI-RS allocation schemes according toexemplary embodiments of the present invention, which are determined byvarious conditions including the CP length, duplex scheme, the number ofOFDM symbols for the downlink (DwPTS) within a special subframe in thecase of TDD, and the existence or absence of duplication allocation AP5.

FIG. 15 is a block diagram illustrating a receiving apparatus to receiveCSI-RSs according to an exemplary embodiment of the present invention.

FIG. 16 is a flowchart illustrating a method for allocating CSI-RSsaccording to an exemplary embodiment of the present invention.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

Exemplary embodiments now will be described more fully hereinafter withreference to the accompanying drawings, in which exemplary embodimentsare shown. This disclosure may, however, be embodied in many differentforms and should not be construed as limited to the exemplaryembodiments set forth therein. Rather, these exemplary embodiments areprovided so that this disclosure will be thorough and complete, and willfully convey the scope of this disclosure to those skilled in the art.Various changes, modifications, and equivalents of the systems,apparatuses, and/or methods described herein will likely suggestthemselves to those of ordinary skill in the art. Elements, features,and structures are denoted by the same reference numerals throughout thedrawings and the detailed description, and the size and proportions ofsome elements may be exaggerated in the drawings for clarity andconvenience.

An embodiment of the present invention provides an apparatus to allocateChannel State Information-Reference Signals (CSI-RSs) to time-frequencyresource areas for each antenna port in a wireless communication system.An embodiment also provides a method for allocating Channel StateInformation-Reference Signals (CSI-RSs) to time-frequency resource areasfor each antenna port in a wireless communication system.

Another embodiment of the present invention provides an apparatus forallocating CSI-RSs to resource areas, so as to enable each cell to havethe orthogonality. An embodiment also provides a method for allocatingCSI-RSs to resource areas, so as to enable each cell to have theorthogonality.

Another embodiment of the present invention provides an apparatus forallocating CSI-RSs to resource areas, so as to enable each cell to havethe orthogonality according to the type of each subframe to which theCSI-RSs will be allocated. An embodiment also provides a method forallocating CSI-RSs to resource areas, so as to enable each cell to havethe orthogonality according to the type of each subframe to which theCSI-RSs will be allocated.

Another embodiment of the present invention provides an apparatus forallocating CSI-RSs to resource areas, so as to enable each cell to havethe orthogonality, according to whether it is possible to duplicatelyallocate a CSI-RS to a reference signal allocated area of a legacycommunication system. An embodiment also provides a method forallocating CSI-RSs to resource areas, so as to enable each cell to havethe orthogonality, according to whether it is possible to duplicatelyallocate a CSI-RS to a reference signal allocated area of a legacycommunication system.

Another embodiment of the present invention provides an apparatus forallocating CSI-RSs to resource areas, so as to enable each cell to havethe orthogonality, according to whether it is possible to allocate aCSI-RS to resource areas allocated for antenna port 5 (AP5) and inconsideration of the subframe structure information including the CPlength, Duplex scheme, and the number of symbols allocated to thedownlink (DwPTS) within a special subframe in the case of TDD. Anembodiment also provides a method for allocating CSI-RSs to resourceareas, so as to enable each cell to have the orthogonality, according towhether it is possible to allocate a CSI-RS to resource areas allocatedfor antenna port 5 (AP5) and in consideration of the subframe structureinformation including the CP length, Duplex scheme, and the number ofsymbols allocated to the downlink (DwPTS) within a special subframe inthe case of TDD.

Another embodiment of the present invention provides an apparatus forallocating CSI-RSs to resource areas, in which, under the condition of asubframe in which the CP is an extended CP, and the duplex scheme isTDD, if CSI-RSs for maximum 8 antenna ports are allocated, the CSI-RSsare allocated to the 8^(th) and 9^(th) symbols (symbol No. l=7 and 8),wherein each CSI-RS for every two antenna ports is allocated to the sameRE while being discriminated from each other by an orthogonal code andneighbor CSI-RS allocated REs in the frequency axis are spaced by aninterval of three REs. An embodiment also provides a method forallocating CSI-RSs to resource areas, in which, under the condition of asubframe in which the CP is an extended CP, and the duplex scheme isTDD, if CSI-RSs for 8 antenna ports are allocated, the CSI-RSs areallocated to the 8^(th) and 9^(th) symbols (symbol No. l=7 and 8),wherein CSI-RSs for every two antenna ports is allocated to the same REwhile being discriminated from each other by an orthogonal code andneighbor CSI-RS allocated REs in the frequency axis are spaced by aninterval of three REs.

Wireless communication systems in the exemplary embodiments are widelyarranged in order to provide various communication services, such asvoice, packet data, etc.

A wireless communication system according to the exemplary embodimentsincludes a UE (User Equipment) and a eNodeB (or BS (Base Station)). Atechnology capable of satisfying an overhead and which may minimize theinterference between cells or antenna ports by using the CSI-RSallocation or mapping as described hereinafter is applied to the UE andthe eNodeB, which will be described below in more detail with referenceto FIG. 1.

As used herein, the UE may refer to a user terminal in a wirelesscommunication system, such as a UE in WCDMA, LTE, HSPA (High SpeedPacket Access), an MS (Mobile Station), a UT (User Terminal), SS(Subscriber Station), and a wireless device in GSM (Global System forMobile Communication).

The eNodeB or cell generally refers to any device, function, orparticular area capable of communicating with the UE, and may be calledby another name, such as Node-B, sector, site, BTS (Base TransceiverSystem), AP (Access Point), or relay node.

That is, as used herein, the eNodeB or cell may have a meaningindicating an area controlled by a BSC (Base Station Controller) of theCDMA, a Node B of the WCDMA, or an area or function covered by a sectoror eNodeB (or site) in the LTE, and may correspond to one of variouscoverage areas, which include a mega cell, a macro cell, a micro cell, apico cell, femto cell, a relay node communication range, etc.

Various multiple access schemes, such as CDMA (Code Division MultipleAccess), TDMA (Time Division Multiple Access), FDMA (Frequency DivisionMultiple Access), OFDMA (Orthogonal Frequency Division Multiple Access),OFDM-FDMA, OFDM-TDMA, and OFDM-CDMA, may be applied to the wirelesscommunication system.

For the uplink transmission and the downlink transmission, it ispossible to use either a TDD (Time Division Duplex) scheme usingdifferent times for transmission or an FDD (Frequency Division Duplex)scheme using different frequencies for transmission.

A wireless communication system may support uplink and/or downlink HARQand can use a Channel Quality Indicator (CQI) for link adaptation.Further, different multiple access schemes may be used for downlinktransmission and uplink transmission. For example, an OrthogonalFrequency Division Multiple Access (OFDMA) scheme may be used for thedownlink, while a Single Carrier-Frequency Division Multiple Access(SC-FDMA) scheme is used for the uplink.

In an exemplary wireless communication system to which embodiments ofthe present invention are applied, one radio frame or wireless frameincludes 10 sub-frames and one sub-frame may include two slots.

The basic unit for data transmission is a sub-frame, and downlink oruplink scheduling is performed by the unit of sub-frame. One slot mayinclude a plurality of OFDM symbols in the time axis and a plurality ofsub-carriers in the frequency axis. Specifically, one slot may include 7or 6 OFDM symbols.

For example, if one sub-frame includes two time slots, each time slotmay include 7 or 6 symbols in the time axis. A time-frequency regiondefined by such a slot as described above and 12 sub-carriers in thefrequency axis may be referred to as a Resource Block (RB).

The transmission time of a radio frame has a length of 10 ms and may bedivided into Transmission Time Intervals (TTIs), each having a durationof 1.0 ms. The terms, “TTI” and “sub-frame”, may be used as have thesame meaning.

As described above, the TTI is a basic transmission unit, and one TTIincludes two time slots, each having the same length, wherein each timeslot may have a duration of 0.5 ms. The time slot includes 7 or 6 LongBlocks (LBs), each of which corresponds to a symbol. The LBs areseparated from each other by Cyclic Prefixes (CPs). In summary, one TTIor sub-frame may include 14 or 12 LB symbols. However, the presentspecification is not limited to the frame, sub-frame, or time-slotstructure as described above.

Each TTI or sub-frame can be divided into 14 or 12 symbols (axes) in thetime axis. Each symbol (axis) can carry one OFDM symbol.

Further, the entire system bandwidth having a length of 20 MHz can bedivided into sub-carriers having different frequencies. For example, anarea, which includes 14 or 12 symbols in the time axis and 12subcarriers (12 consecutive subcarriers within one TTI) in the frequencyaxis, may be referred to as a pair of Resource Block (RB).

For example, the bandwidth of 10 MHz within one TTI may include 50 RBpairs in the frequency axis.

In the RB structure shaped like a grid as described above, each unitspace shaped like a grid cell is referred to as a Resource Element (RE),and each subframe or Resource Block (RB) pairs having the structure asdescribed above may include a total of 168 REs (=14 symbols×12sub-carriers) or 144 REs (=12 symbols×12 sub-carriers).

In the LTE communication system, the downlink reference signals includea Cell-specific Reference Signal (CRS), a Multicast/Broadcast overSingle Frequency Network (MBSFN) reference signal, and a UE-specificreference signal (DM-RS reference signal) are defined.

Among those reference signals, the CRS reference signal may be used forunicast transmission rather than MBSFN transmission, and thus, may beincluded in and transmitted by all downlink subframes within a cellwhich does not support the MBSFN transmission. Further, the CRS may betransmitted through one or multiple antennas from among antenna portnumber 0 to 3.

Further, one reference signal is transmitted through each downlinkantenna port, and an RE used for transmission of an RS through one portfrom among the antenna ports within a slot may not be used for anotherantenna port within the same slot.

It is possible to provide an example in which CRSs are mapped totime-frequency REs different according to four different antenna ports.In each antenna port, the REs, to which CRSs are allocated, may have acycle of 6 REs for the sub-carriers.

Some next generation communication technologies support a maximum ofeight antennas in the downlink. That is, the CRSs defined for the fourexisting antennas are insufficient for detection of channel informationat the time of downlink transmission. To this end, a reference signalnamed “Channel State Information-Reference Signal (CSI-RS)” is newlydefined in order to obtain channel state information for a maximum ofeight antennas in the downlink.

According to the current discussion in the LTE-A, CSI-RSs are mapped toone RE for each antenna port in an area including 12 sub-carrierscorresponding to one RB pairs along the frequency axis and at everypredetermined cycle along the time axis for each cell. Thus, for a totalof eight antenna ports, a maximum of 8 REs are allocated andtransmitted. In this event, the predetermined cycle corresponds to amultiple of the time of 5 ms including 5 subframes (that is, thepredetermined cycle may be 5 ms, 10 ms, etc.). If the predeterminedcycle is 5 ms, the CSI-RSs are transmitted by a total of two subframesamong the 10 subframes within one radio frame corresponding to 10 ms.Therefore, once the CSI-RS pattern for one subframe is defined, theCSI-RSs can be allocated to the other subframes with a predeterminedcycle.

A communication system using a maximum of 8×8 Multiple Input MultipleOutput (MIMO) antennas at both the transmission port and the receptionport is disclosed. In this system, since CSI-RSs being differentaccording to the antenna ports or antenna layers are transmitted, atransmitter may allocate CSI-RSs for a total of eight antenna ports to atime-frequency domain in a discriminatory manner. Thus, the CSI-RSs maybe allocated in a manner capable of discriminating cells from each otherin the multi-cell environment.

In the present specification, antenna layers refer to data layers whichcan be logically simultaneously transmitted from an eNodeB or a UE tomultiple antenna ports. However, the antenna layers may have the samedata or different data. Therefore, the number of the antenna layers maybe equal to or smaller than the number of antenna ports.

The following description is based on the antenna port, although it canbe applied to the antenna layer.

As noted from the above discussion, the basic definition on the CSI-RSand the overhead of each antenna port for one subframe has beendisclosed. However, a method for allocation and transmission of acorresponding reference signal pattern according to each antenna port ineach eNodeB (or cell) has not been specifically disclosed. Therefore, amethod of configuring a CSI-RS pattern for at least one subframe willnow be disclosed.

An example of REs usable for the CSI-RSs may be obtained by using thedefinition as described above. For a single subframe, and specificallyin the case of normal subframe, locations of existing CRSs, the controlregion, and the LTE Rel-9/10 DM-RS (Demodulation Reference Signal),among a total of 14 symbols are taken into consideration. Based on thisconsideration, CSI-RSs may be allocated to and transmitted by the10^(th) or 11^(th) symbol so as to prevent overlapping with the existingCRSs.

Further, for the normal subframe, a scheme different from the methoddescribed above may be used in determining REs usable for the CSI-RSs inthe case of considering even the DM-RS of Rel-8.

For one subframe, it is important to allocate a CSI-RS pattern which hasan orthogonality for each antenna port. However, if eNodeBs (or cells)are distinguished only by CSI-RS sequences mapped to defined CSI-RSpatterns, it may cause many neighbor cells to simultaneously transmitCSI-RSs through the same time-frequency resource, resulting ininterference between neighbor cells. This may cause significantperformance degradation. Throughout this disclosure, the term“orthogonality” may refer to perfect orthogonality, but is notnecessarily limited as such.

Particularly, in a communication system such as a Cooperative MultipointTx/Rx System (CoMP), where a user transmits/receives a reference signalto/from a neighbor cell as well as a serving cell, with which the useris currently performing transmission/reception, reception power of aCSI-RS of the neighbor cell is weaker than that of the serving cell.Therefore, if the serving cell and the neighbor cell simultaneouslytransmit CSI-RSs through the same time-frequency resource, the user mayhave difficulty in properly detecting the CSI-RS from the neighbor cell.

Accordingly, this embodiment may provide a scheme, in which a CSI-RS isallocated (or mapped) and then transmitted with a orthogonality withrespect to time-frequency resources for each cell, thereby reducing theperformance degradation caused by interference between neighbor cells.

The CP length, Duplex scheme (TDD or FDD), etc. may change the structureof the subframe. The present embodiment presents a method of allocatingor mapping and transmitting CSI-RSs while enabling each cell (or cellgroup) to have a orthogonality with respect to time-frequency resourcesfor each of the various types of subframes.

Therefore, an embodiment of the present invention may include the stepsof: receiving an input of subframe structure information of a subframeto be allocated a CSI-RS, a cell ID (Identifier), eNodeB (or cell)information including bandwidth information or antenna port number of aneNB, and system information including a subframe number; and allocatingCSI-RSs of each antenna port to resource areas while one or more cells(or cell groups) to have an orthogonality in frequency/time resources byusing the subframe structure information and the system information.

The subframe structure information may include CP length information andDuplex scheme information (FDD/TDD). If the Duplex scheme is TDD, one ortwo special subframe(s) in a radio frame may include the number of OFDMsymbols for the downlink (DwPTS) within a special subframe, and the stepof allocating the CSI-RSs may include an additional consideration onwhether to use AP (antenna port) 2 and AP (antenna port) 3 correspondingto the third and fourth CRS antenna ports.

FIG. 1 is a block diagram illustrating a structure of a CSI-RSallocation apparatus according to an exemplary embodiment of the presentinvention.

Referring to FIG. 1, a CSI-RS allocation apparatus 100 includes a CSI-RSgenerator 110 and a CSI-RS resource allocator 120.

The CSI-RS generator 110 receives information, such as subframestructure information and system information, and generates a CSI-RS ora CSI-RS sequence based on the received information. The subframestructure information reflects one or more combinations of the CP lengthor CP structure method (Normal CP or Extended CP) within a subframe andthe number of used antennas of each existing CRS or DM-RS (inculdingRel-8 DM-RS), in order to detect the structure of the subframe to whichthe CSI-RS is currently applied and generate a CSI-RS pattern proper forthe detected structure. The system information may include one or morecombinations of eNodeB (or cell) information, relay node information, UEinformation, and subframe number. The eNodeB (or cell) information, forexample, may be eNodeB (or cell) antenna information, eNodeB (or cell)bandwidth information, and cell ID information. The system informationmay include a cell ID, so as to enable the configuration of a CSI-RScapable of identifying each cell group.

For example, the CSI-RS generator 110 determines a length of a sequenceby using system-specific information such as bandwidth information of aneNodeB, and receives cell ID information and selects a CSI-RS of acorresponding cell ID which has been predetermined.

The CSI-RS resource allocator 120 receives the subframe structureinformation, the system information, and the frame timing information,and allocates CSI-RSs according to antenna ports, which have beengenerated by the CSI-RS generator 110, to time-frequency resourceelements. Thereafter, the CSI-RSs allocated to REs are multiplexed witheNodeB transmission frames.

The CSI-RS resource allocator 120 performs a basic function forallocating resources of an OFDM symbol (the x-axis) and a subcarrierlocation (the y-axis) by a predetermined rule in a resource allocationmethod for CSI-RSs, and multiplexing allocated resources with eNodeBtransmission frames at predetermined frame timing.

If allocating CSI-RSs for each of a maximum of 8 antenna ports to atime-frequency domain, the CSI-RS resource allocator 120 according tothis embodiment allocates CSI-RSs of each antenna port to time-frequencyresource elements while securing orthogonality for each cell (or cellgroup) according to the subframe type determined depending on thesubframe structure information, and system information such as cell ID.

FIGS. 2 to 14 illustrate various CSI-RS allocation schemes according tothe first to eighth embodiments according to exemplary embodiments ofthe present invention, which are determined by various conditionsincluding the CP length, duplex scheme, the number of OFDM symbols forthe downlink (DwPTS) within a special subframe in the case of TDD, andthe existence or absence of duplication allocation of AP5.

A CSI-RS for a particular antenna port can be allocated in such a manneras to have frequency shifts in the direction of the frequency axisaccording to cells (or cell groups). Particularly, if there are 8antenna ports for the CSI-RSs, the CSI-RS allocation may have threetypes of shifts along the frequency axis. Specifically, CSI-RSs of thesame antenna port may be allocated with a shift by one subcarrier or REin the direction of the frequency axis for each of 3 cells (or cellgroups), so that the cells (or cell groups) can have distinguishableCSI-RS allocation patterns, respectively. Further, if there are 8antenna ports for the CSI-RSs, the cells (or cell groups) may havedistinguishable CSI-RS allocation patterns for each of two or threecells (or cell groups), through two or three types of shifts along thesymbol axis and the frequency axis.

The embodiments for the CSI-RS allocation to subframes withdiscrimination between cells (or cell groups) according to whether thereis a duplicated allocation (allocation with consideration) of AP5, andaccording to each subframe structure by the number of OFDM symbols forthe downlink (DwPTS) within a special subframe if the Duplex scheme isTDD, and the CP length will be described in more detail with referenceto FIGS. 2 to 11.

A wireless communication system, to which embodiments of the presentinvention are applied, includes a CSI-RS allocation apparatus 100according to this embodiment as shown in FIG. 1. The CSI-RS allocationapparatus may include a CSI generator 110 and a CSI-RS resourceallocator 120.

The wireless communication system may further include a scrambler, amodulation mapper, a layer mapper, a precoder, an RE mapper, an OFDMsignal generator, etc., which are elements of a basic transmissionapparatus. However, the structure as described above is not essential inthis embodiment.

This wireless communication system may be a communication system of theeNodeB.

A basic operation of the wireless communication system will now bedescribed. Bits, which go through channel coding and are input in theform of codeword in a downlink, are scrambled by the scrambler, and arethen input to the modulation mapper. The modulation mapper modulates thescrambled bits to a complex modulation symbol. The layer mapper maps thecomplex modulation symbol to a single or multiple transmission layer(s).The precoder precodes the complex modulation symbol over eachtransmission channel of an antenna port. Thereafter, the RE mapper mapsthe complex modulation symbol for each antenna port to a relevantresource element.

In this embodiment, the CSI-RS generator generates a CSI-RS, andprovides the generated CSI-RS to the CSI-RS resource allocator. TheCSI-RS resource allocator, individually or in conjunction with theresource element mapper, allocates CSI-RSs according to antenna ports toa time-frequency domain in the scheme as described above, andmultiplexes the allocated CSI-RSs with eNodeB transmission frames at apredetermined timing.

Thereafter, the OFDM signal generator generates a complex time domainOFDM signal for each antenna port, and transmits the generated complextime domain OFDM signal through the relevant antenna port.

The CSI-RS allocation apparatus and the resource element mapper may beimplemented through integration of them by hardware or software.

A CSI-RS allocation scheme as shown in FIG. 2 may be applied to atypical structure, such as subframe structure according to the FDDscheme of a normal CP.

According to the CSI-RS allocation scheme as shown in FIG. 2, CSI-RSsare allocated to time-frequency resource areas for each of a maximum of8 antenna ports, wherein the CSI-RSs of the antenna port are allocatedto four REs or subcarriers by the unit of one symbol (symbol axis)within one subframe, and neighbor CSI-RS allocated REs or subcarriersare spaced with an interval of three REs or subcarriers. In this event,the CSI-RSs are allocated to a total of two symbols (symbol axes) withinone subframe (for example, the CSI-RSs may be allocated to the 10^(th)and 11^(th) OFDM symbols as shown in FIG. 2), each of the CSI-RSs withrespect to each of a total of eight antenna ports is duplicatelyallocated to two REs while being discriminated from CSI-RSs of anotherantenna port by an orthogonal code. That is, a total of eight antennaports is tied into four pairs, which are discriminated from each otherthrough FDM, and two antenna ports within each pair are discriminatedfrom each other by CDM (CDM-T) using an orthogonal code such as theOrthogonal Cove Code (OCC).

In this event, the CSI-RS resource allocator performs the allocationwhile causing a shift of a CSI-RS for a particular antenna port in thedirection of frequency axis for each cell (or cell group). Further, theCSI-RS resource allocator may perform the blanking, which empties theREs, in which another cell group except for its own cell group (the cellgroup to which the serving cell belongs) sends CSI-RSs, without sendingdata to the REs, or the muting, which performs the transmission usingzero power. That is, the CSI-RS resource allocator performs theallocation while causing a frequency shift of CSI-RSs of the sameantenna port for each cell (cell group). Further, the CSI-RS resourceallocator performs the allocation while causing CSI-RSs of the sameantenna port to make a frequency shift by one subcarrier or RE in thedirection of the frequency axis for each of 3 cells (or cell groups), sothat at least three cell groups within one subframe can havedistinguished CSI-RS allocation patterns.

Although FIG. 2 shows a method of configuring a CSI-RS for apredetermined subframe, this method applies to a case corresponding to anormal CP and an FDD among various subframe structures. Therefore, ascheme may be arranged to configure a CSI-RS for the other subframestructure includes an extended CP or the duplex scheme is TDD. Further,although the method shown in FIG. 2 does not take AP5 (antenna port No.5), which is an LTE Rel-8 DM-RS, into consideration, the existence ofAP5 may be considered in configuring the CSI-RS if a legacy impact bythe AP5 is big.

Therefore, embodiments of the present invention as shown in FIGS. 2 to11 present a method for CSI-RS allocation and transmission, which mayreduce the performance degradation due to interference between neighborcells in various subframe structures, through the CSI-RS allocation andtransmission with an orthogonality (an orthogonality in view oftime/frequency resources) for each of multiple cell groups according toeach subframe structure, such as information on whether there is aduplicated allocation (allocation with consideration) of AP5, the Duplexscheme (FDD/TDD), and the CP length.

Especially, under the condition of a subframe as in the embodiment shownin FIG. 10, in which the CP is an extended CP, the duplex scheme is TDD,and a duplicated allocation to AP5 is allowed, if CSI-RSs for maximum 8antenna ports are allocated, the CSI-RSs may be allocated to the 8th and9th symbols (symbol No. l=7 and 8), in such a manner that CSI-RSs forevery two antenna ports are allocated to the same RE while beingdiscriminated from each other by an orthogonal code and neighbor CSI-RSallocated REs are spaced by an interval of three REs, which thus includetwo empty REs between two CSI-RS allocated REs.

FIGS. 2 to 11 illustrate various CSI-RS allocation schemes under variousconditions including the CP length, duplex scheme, and consideration ornon-consideration of AP5 according to embodiments of the presentinvention.

AP0, AP1, AP2, and AP3 are antenna ports for CRS, and AP5 is an antennaport for Rel-8 DM-RS. If only two antennas are used for the CRS, onlyAP0 and AP1 are used and AP2 and AP3 are not used. In the case of TDD,differently from FDD, a total of 10 subframes include downlink subframesand uplink subframes, which are separately arranged, and one or twospecial subframe(s), which separately includes an OFDM symbol for thedownlink (DwPTS), a Guard Band (GB), and an OFDM symbol for the uplink(UpPTS) within a special subframe. The OFDM symbol for the downlink(DwPTS) within the special subframe has different lengths according tothe special subframe mode and/or according to whether the configuredsubframe includes a normal CP or an extended CP. For example, in thecase of a normal CP, the number of OFDM symbols for the downlink withinthe special subframe is one of the numbers 3, 9, 10, 11, and 12, amongthe total of 14 symbols. In the case of the extended CP, the number ofOFDM symbols for the downlink within the special subframe is one of thenumbers 3, 8, 9, or 10. However, the present invention is not limited tothese numbers.

In this event, FS 1 (Frame Structure type 1) means FDD, and FS 2 (FrameStructure type 2) means TDD.

FIG. 2 shows a CSI-RS allocation scheme according to a first embodimentof the present invention, for a downlink subframe in which the CP is anormal CP and the duplex scheme is FDD or TDD.

Further, in the first embodiment of the present invention as shown inFIG. 2, a duplicated allocation of AP5 is allowed (that is, CSI-RSallocation to the location of AP5 is allowed), without consideration onwhether to use AP2 or AP3 (that is, it is the same regardless of eitherif AP2 or AP3 is used or if AP2 or AP3 is not used).

The following configuration is applied to the first embodiment of thepresent invention.

Two consecutive OFDM symbols are used, which may include the 10^(th) andthe 11^(th) symbols (i.e. l=9 and 10).

Every two antenna ports are tied into one pair, and pairs aremultiplexed by FDM while two consecutive OFDM symbols for two antennaports within each pair are multiplexed by CDM (i.e. CDM-T) by using anorthogonal code such as the Orthogonal Cove Code (OCC).

In the present embodiment, the orthogonal code may be a code having theorthogonality, such as a two digit Walsh Code. That is, in FIG. 2, theCSI-RS of antenna port indicated on the preceding RE may be identifiedby orthogonal code 1 (OCC 1), such as [1, 1], while the CSI-RS ofantenna port indicated on the following RE may be identified byorthogonal code 2 (OCC 2), such as [1, −1].

In FIGS. 2 to 11, REs having numbers recorded thereon correspond to REsto which CSI-RSs are allocated, and the numbers correspond to numbers ofantenna ports to which the CSI-RSs are allocated.

Antenna ports for 2/4/8 CSI-RSs may be allocated to two symbols (even if3/5/7 antenna ports are allocated, with the addition of one more antennaport to the corresponding number of antenna ports to make the evenCSI-RSs antenna ports. That is, if 7 antenna ports are allocated, 8antenna ports are considered for the CSI-RS configuration, which resultsin that the number of antenna ports is 8 and one half of the number ofantenna ports is 4), and the CSI-RSs are allocated to REs correspondingto one half of the number of antenna ports for each symbol. For example,if antenna ports for 8 CSI-RSs are allocated, CSI-RSs for each antennaport are allocated to 4 REs (or subcarriers) in each symbol.

An interval of REs corresponding to “24/(number of antenna ports)” alongthe frequency axis is arranged between neighbor CSI-RS allocated REs forone symbol axis. For example, if antenna ports for 8 CSI-RSs areallocated, an interval of 3 REs along the frequency axis is established(which implies that 2 empty REs exist) between neighbor CSI-RS allocatedREs for one symbol axis.

According to the cell group ID, a frequency shift may occur by the unitof a total of 12 subcarriers. In this event, based on the intervalbetween neighbor CSI-RS allocated REs, it is possible to generate cellgroup-specific patterns (reuse factor having the orthogonality), whichare discriminated from each other and correspond to a maximum of“24/(number of antenna ports)”, within one subframe. In this event, forexample, if antenna ports for 8 CSI-RSs are allocated, it is possible togenerate a total of three cell group-specific patterns, which areperfectly discriminated from each other, within one subframe.

Among the REs, it is possible to perform the blanking, which empties theREs, to which another cell group except for its own cell group (the cellgroup to which the serving cell belongs) sends CSI-RSs, without sendingdata to the REs, or the muting, which performs the transmission usingzero power.

The CSI-RS allocation scheme according to the first embodiment of thepresent invention as described above can be expressed by Equation 1below. Equation 1 below shows a representative example for helping theunderstanding of the present invention and may be expressed in anotherway within the range capable of maintaining the basic scheme describedabove.

-   -   CSI-RS antenna port=1, 3, 5, 7:OCC [+1,+1]    -   CSI-RS antenna port=2, 4, 6, 8:OCC [+1,−1]

$\begin{matrix}{{k = {{12 \cdot m} + {\left( {v + v_{shift}} \right){mod}\; 12}}}{{l = 9},10}} & \left\lbrack {{Equation}\mspace{14mu} 1} \right\rbrack \\{{{m = 0},1,2,\ldots \mspace{14mu},{N_{RB}^{DL} - 1}}{v = \left\{ {{\begin{matrix}0 & {{{{if}\mspace{14mu} {CSI}\text{-}{RS}\mspace{14mu} {antenna}\mspace{14mu} {port}} = 1},2} \\6 & {{{{if}\mspace{14mu} {CSI}\text{-}{RS}\mspace{14mu} {antenna}\mspace{14mu} {port}} = 3},4} \\3 & {{{{if}\mspace{14mu} {CSI}\text{-}{RS}\mspace{14mu} {antenna}\mspace{14mu} {port}} = 5},6} \\9 & {{{{if}\mspace{14mu} {CSI}\text{-}{RS}\mspace{14mu} {antenna}\mspace{14mu} {port}} = 7},8}\end{matrix}v_{shift}} = {N_{ID}^{cell}\; {mod}\; 12}} \right.}} & \;\end{matrix}$

In Equation 1, k indicates a subcarrier number, l indicates a symbolnumber, N_(ID) ^(cell) indicates a cell ID, and N_(RB) ^(DL) indicatesthe number of RBs in the downlink.

In this event, the number of antenna port, in which the CSI-RS isduplicately allocated to the same RE, and the sequence of the numbers ofantenna ports in the frequency direction may change and are not limitedby the example shown in FIG. 2. That is, in FIG. 2, as the index of thesubcarrier increases, the allocation is performed in the sequence of(1,2), (5,6), (3,4), and (7,8). However, this is not an inevitablecondition and another antenna port combination or another sequence, suchas (1,2), (3,4), (5,6), and (7,8), may be employed for the allocation,if the index of the subcarrier increases or decreases.

However, as shown in FIG. 2, antenna ports duplicately allocated to oneRE may be neighbor antenna ports adjacent to each other. That is, inFIG. 2, the antenna ports duplicately allocated to (l, k)=(9 and 10, 0)may be antenna port 1 and antenna port 2, which are neighbor or adjacentto each other.

As described above, in the first embodiment of the present invention asshown in FIG. 2, CSI-RSs of (1,2), (5,6), (3,4), and (7,8) are allocatedto the locations where k=0, 3, 6, and 9, respectively, in the symbolaxes of (l=9 and 10) in cell group A, CSI-RSs of (1,2), (5,6), (3,4),and (7,8) are allocated to the locations where k=1, 4, 7, and 10,respectively, which are shifted by +1 along the frequency axis, in thesame symbol axis in cell group B, and CSI-RSs of (1,2), (5,6), (3,4),and (7,8) are allocated to the locations where k=2, 5, 8, and 10,respectively, in cell group C.

However, the combination and the sequence of the antenna port numbersarranged in the frequency direction are not necessarily limited to FIG.2, and another combination or sequence may be employed.

FIG. 3 shows a CSI-RS allocation scheme according to a second embodimentof the present invention, for a downlink subframe in which the CP is anormal CP and the duplex scheme is FDD or TDD, as in the firstembodiment shown in FIG. 2.

However, although a duplicated allocation of AP5 is allowed in the firstembodiment of the present invention, a duplicated allocation of AP5 isnot allowed in the second embodiment of the present invention as shownin FIG. 3.

In the second embodiment of the present invention, whether to use AP2 orAP3 is not considered (that is, it is the same regardless of either ifAP2 or AP3 is used or if AP2 or AP3 is not used).

The following configuration is applied to the second embodiment of thepresent invention.

-   -   Two consecutive OFDM symbols are used, and the CSI-RSs are        allocated to two different consecutive symbol axes according to        the cell.    -   It is the same as in the first embodiment of the present        invention shown in FIG. 2 in view of that an antenna port is        identified by an OCC code and the CSI-RSs are allocated to REs        corresponding to one half of the number of antenna ports for        each symbol in the second embodiment of the present invention.    -   For a total of three basic cell groups, CSI-RSs may be        configured. In the first cell group, CSI-RSs are allocated to        the 10th and 11th symbol axes and to the other REs except for        the REs, at which AP5 is located, in the 10th and 11th symbol        axes. In the second cell group, CSI-RSs are allocated to the 6th        and 7th symbol axes and to the other REs except for the REs, at        which AP5 and Rel-9/10 DM-RS are located. In the third cell        group, CSI-RSs are allocated to the 13th and 14th symbol axes        and to the other REs except for the REs, at which AP5 and        Rel-9/10 DM-RS are located. In this event, a CSI-RS allocation        pattern corresponding to each cell group may be generated by a        time/frequency shift of a CSI-RS allocation pattern        corresponding to another cell group. For example, the CSI-RS        allocation pattern corresponding to the second cell group may be        generated by shifting the CSI-RS allocation pattern        corresponding to the first cell group by −4 in the OFDM symbol        axis corresponding to time and by +1 in the subcarrier axis        corresponding to frequency.

If 8 CSI-RS antenna ports are used, it is possible to generate threediscriminated cell group-specific patterns (reuse factors having theorthogonality) within one subframe. If two or four CSI-RS antenna portsare used, it is possible to generate 12 or 6 cell group-specificpatterns (reuse factors having the orthogonality), which arediscriminated from each other, within one subframe.

Further, the construction capable of muting or blanking REs, to whichCSI-RSs of another cell (cell group) are allocated, is also the same asthat in the first embodiment shown in FIG. 2.

The CSI-RS allocation scheme according to the second embodiment of thepresent invention shown in FIG. 3 can be expressed by Equation 2 below.Equation 2 below shows a representative example for helping theunderstanding of the present invention and may be expressed in anotherway within the range capable of maintaining the basic scheme describedabove.

-   -   CSI-RS antenna port=1, 3, 5, 7:OCC [+1,+1]    -   CSI-RS antenna port=2, 4, 6, 8:OCC [+1,−1]

$\begin{matrix}{{k = {{12 \cdot m} + {\left( {v + v_{shift}} \right){mod}\; 12}}}{l = \left\{ {{{\begin{matrix}{9,10} & {{{if}\mspace{14mu} N_{ID}^{cell}{mod}\; 3} = 0} \\{5,6} & {{{if}\mspace{14mu} N_{ID}^{cell}{mod}\; 3} = 1} \\{12,13} & {{{if}\mspace{14mu} N_{ID}^{cell}{mod}\; 3} = 2}\end{matrix}m} = 0},1,2,\ldots \mspace{14mu},{{N_{RB}^{DL} - {1v}} = \left\{ {{\begin{matrix}2 & {{{{if}\mspace{14mu} {CSI}\text{-}{RS}\mspace{14mu} {antenna}\mspace{14mu} {port}} = 1},2} \\6 & {{{{if}\mspace{14mu} {CSI}\text{-}{RS}\mspace{14mu} {antenna}\mspace{14mu} {port}} = 3},4} \\3 & {{{{if}\mspace{14mu} {CSI}\text{-}{RS}\mspace{14mu} {antenna}\mspace{14mu} {port}} = 5},6} \\7 & {{{{if}\mspace{14mu} {CSI}\text{-}{RS}\mspace{14mu} {antenna}\mspace{14mu} {port}} = 7},8}\end{matrix}v_{shift}} = \left\{ \begin{matrix}0 & {{{if}\mspace{14mu} N_{ID}^{cell}{mod}\; 3} = 0} \\1 & {else}\end{matrix} \right.} \right.}} \right.}} & \left\lbrack {{Equation}\mspace{14mu} 2} \right\rbrack\end{matrix}$

In this event, the change in the number of an antenna port, in which theCSI-RS is duplicately allocated to the same RE, and the sequence of thenumbers of antenna ports in the frequency direction may be similar tothat of the first embodiment shown in FIG. 2.

Further, although FIG. 3 shows combinations of four REs, which includecombinations of (1,2)+(5,6) and (3,4)+(7,8), the present invention isnot limited to the combinations shown in FIG. 3, and may employ anothercombination or sequence.

In conclusion, according to the second embodiment shown in FIG. 3, twoconsecutive cell group-specific symbol axes are used, wherein one cellgroup A may be shifted by −1 from the other cell groups B and C in thefrequency axis.

FIG. 4 shows a CSI-RS allocation scheme according to a third embodimentof the present invention, for a subframe in which the CP is a normal CP,the duplex scheme is TDD, and the number of OFDM symbols allocated tothe downlink (DwPTS) within the subframe is 11 or 12. In this event, thesubframe may be the special subframe in TDD as described above.

Further, in the third embodiment of the present invention, duplicatedallocation of AP5 is allowed, and whether to use AP2 or AP3 is notconsidered.

The following configuration is applied to the third embodiment of thepresent invention shown in FIG. 4.

Two consecutive OFDM symbols are used, which may include the 6th and the7th symbols (i.e. l=5 and 6).

It is the same as in the first embodiment of the present invention shownin FIG. 2 in view of that an antenna port is identified by an OCC codeand the CSI-RSs are allocated to REs corresponding to one half of thenumber of antenna ports for each symbol in the second embodiment of thepresent invention.

As in the first embodiment, an interval of REs corresponding to“24/(number of antenna ports)” along the frequency axis is arrangedbetween neighbor CSI-RSs allocated REs for one symbol axis.

As in the first embodiment shown in FIG. 2, according to the cell groupID, it is possible to generate cell group-specific patterns, which arediscriminated from each other and correspond to a maximum of “24/(numberof antenna ports)”, within one subframe. Further, the constructioncapable of muting or blanking REs, to which CSI-RSs of another cell (orcell group) are allocated, is also the same as that in the firstembodiment shown in FIG. 2.

The CSI-RS allocation scheme according to the third embodiment of thepresent invention shown in FIG. 4 can be expressed by Equation 3 below.Equation 3 below shows a representative example for helping theunderstanding of the present invention and may be expressed in anotherway within the range capable of maintaining the basic scheme describedabove.

-   -   CSI-RS antenna port=1, 3, 5, 7:OCC [+1,+1]    -   CSI-RS antenna port=2, 4, 6, 8:OCC [+1,−1]

$\begin{matrix}{{k = {{12 \cdot m} + {\left( {v + v_{shift}} \right){mod}\; 12}}}{{l = 5},6}{{m = 0},1,2,\ldots \mspace{14mu},{N_{RB}^{DL} - 1}}{v = \left\{ {{\begin{matrix}0 & {{{{if}\mspace{14mu} {CSI}\text{-}{RS}\mspace{14mu} {antenna}\mspace{14mu} {port}} = 1},2} \\6 & {{{{if}\mspace{14mu} {CSI}\text{-}{RS}\mspace{14mu} {antenna}\mspace{14mu} {port}} = 3},4} \\3 & {{{{if}\mspace{14mu} {CSI}\text{-}{RS}\mspace{14mu} {antenna}\mspace{14mu} {port}} = 5},6} \\9 & {{{{if}\mspace{14mu} {CSI}\text{-}{RS}\mspace{14mu} {antenna}\mspace{14mu} {port}} = 7},8}\end{matrix}v_{shift}} = {N_{ID}^{cell}\; {mod}\; 12}} \right.}} & \left\lbrack {{Equation}\mspace{14mu} 3} \right\rbrack\end{matrix}$

In this event, as in the first embodiment shown in FIG. 2, the number ofantenna port, in which the CSI-RS is duplicately allocated to the sameRE, and the sequence of the numbers of antenna ports in the frequencydirection may change differently from those in FIG. 4.

Further, the frequency shift of each cell group is not limited to thestructure shown in FIG. 4. Also, the combination and the sequence of theantenna port numbers arranged in the frequency direction are notnecessarily limited to FIG. 4 and another combination or sequencedifferent from that shown in FIG. 4 may be employed.

FIG. 5 shows a CSI-RS allocation scheme according to a fourth embodimentof the present invention, for a subframe in which the CP is a normal CP,the duplex scheme is TDD, and the number of OFDM symbols allocated tothe downlink (DwPTS) within the subframe is 11 or 12, as in the thirdembodiment of the present invention. However, in the fourth embodimentof the present invention, duplicated allocation of AP5 is not allowed,

In this event, the subframe may be the special subframe as describedabove.

Further, in the fourth embodiment of the present invention, whether touse AP2 or AP3 is not considered.

The following configuration is applied to the fourth embodiment of thepresent invention shown in FIG. 5.

Two consecutive OFDM symbols are used, and the CSI-RSs may be allocatedto two different consecutive symbol axes according to the cell.

It is similar to the first embodiment of the present invention, shown inFIG. 2, in view of that an antenna port is identified by an OCC code andthe CSI-RSs are allocated to REs corresponding to one half of the numberof antenna ports for each symbol in the second embodiment of the presentinvention.

CSI-RSs may be configured for a total of three basic cell groupsdiscriminated from each other. In the first cell group, CSI-RSs areallocated to the 6th and 7th symbol axes and to the other REs except forthe REs, at which AP5 is located, in the 6th and 7th symbol axes. In thesecond cell group, CSI-RSs are allocated to the 3rd and 4th symbol axesand to the other REs except for the REs, at which AP5 and Rel-9/10 DM-RSare located, in the 3rd and 4th symbol axes. In the third cell group,CSI-RSs are allocated to the 10th and 11th symbol axes and to the otherREs except for the REs, at which AP5 and Rel-9/10 DM-RS are located, inthe 10th and 11th symbol axes. In this event, a CSI-RS allocationpattern corresponding to each cell group may be generated by atime/frequency shift of a CSI-RS allocation pattern corresponding toanother cell group. For example, the CSI-RS allocation patterncorresponding to the second cell group may be generated by shifting theCSI-RS allocation pattern corresponding to the first cell group by −3 inthe OFDM symbol axis corresponding to time and by −2 in the subcarrieraxis corresponding to frequency.

If 8, 4, and 2 CSI-RS antenna ports are used, it is possible to generate3, 6, and 12 discriminated cell group-specific patterns (reuse factorshaving the orthogonality) within one subframe, respectively, similarlyto the second embodiment shown in FIG. 3. Further, the constructioncapable of muting or blanking REs, to which CSI-RSs of another cell(cell group) are allocated, is also the same as that in the secondembodiment shown in FIG. 3.

The CSI-RS allocation scheme according to the fourth embodiment of thepresent invention shown in FIG. 5 can be expressed by Equation 4 below.Equation 4 shows a representative example for helping the understandingof the present invention and may be expressed in another way within therange capable of maintaining the basic scheme described above.

-   -   CSI-RS antenna port=1, 3, 5, 7:OCC [+1,+1]    -   CSI-RS antenna port=2, 4, 6, 8:OCC [+1,−1]

$\begin{matrix}{{k = {{12 \cdot m} + {\left( {v + v_{shift}} \right){mod}\; 12}}}{l = \left\{ {{{\begin{matrix}{5,6} & {{{if}\mspace{14mu} N_{ID}^{cell}{mod}\; 3} = 0} \\{2,3} & {{{if}\mspace{14mu} N_{ID}^{cell}{mod}\; 3} = 1} \\{9,10} & {{{if}\mspace{14mu} N_{ID}^{cell}{mod}\; 3} = 2}\end{matrix}m} = 0},1,2,\ldots \mspace{14mu},{{N_{RB}^{DL} - {1v}} = \left\{ {{\begin{matrix}4 & {{{{if}\mspace{14mu} {CSI}\text{-}{RS}\mspace{14mu} {antenna}\mspace{14mu} {port}} = 1},2} \\9 & {{{{if}\mspace{14mu} {CSI}\text{-}{RS}\mspace{14mu} {antenna}\mspace{14mu} {port}} = 3},4} \\5 & {{{{if}\mspace{14mu} {CSI}\text{-}{RS}\mspace{14mu} {antenna}\mspace{14mu} {port}} = 5},6} \\11 & {{{{if}\mspace{14mu} {CSI}\text{-}{RS}\mspace{14mu} {antenna}\mspace{14mu} {port}} = 7},8}\end{matrix}v_{shift}} = \left\{ \begin{matrix}0 & {{{if}\mspace{14mu} N_{ID}^{cell}{mod}\; 3} = 0} \\{- 2} & {else}\end{matrix} \right.} \right.}} \right.}} & \left\lbrack {{Equation}\mspace{14mu} 4} \right\rbrack\end{matrix}$

The number of antenna port, in which the CSI-RS is duplicately allocatedto the same RE, and the sequence of the numbers of antenna ports in thefrequency direction may change, as in the first embodiment shown in FIG.2.

Further, although FIG. 5 shows a scheme of allocating a combination of(1,2)+(5,6) to four neighbor REs while allocating (3,4) and (7,8) tospaced REs, the present invention is not limited to the scheme shown inFIG. 5 and may employ another combination or sequence.

Thus, according to the fourth embodiment shown in FIG. 5, twoconsecutive cell group-specific symbol axes are used, wherein one cellgroup A may be shifted by +2 from the other cell groups B and C in thefrequency axis.

FIG. 6 shows a CSI-RS allocation scheme according to a fifth embodimentof the present invention, for a subframe in which the CP is a normal CP,the duplex scheme is TDD, and the number of OFDM symbols allocated tothe downlink (DwPTS) within the subframe is 9 or 10.

In this event, the subframe is the special subframe as described above.

Further, in the fifth embodiment of the present invention, duplicatedallocation of AP5 is allowed, and whether to use AP2 or AP3 is notconsidered.

The following configuration is applied to the fifth embodiment of thepresent invention shown in FIG. 6.

Four OFDM symbols are used, which may include the 3rd, 4th, 6th, and the7th symbols, in cooperation with Rel-9/10 DM-RS.

It is the same as in the first embodiment of the present invention shownin FIG. 2 in view of that an antenna port is identified by an OCC codeand the CSI-RSs are allocated to REs corresponding to one half of thenumber of antenna ports for each symbol in the second embodiment of thepresent invention.

-   -   According to the cell group ID, a frequency shift may occur.        Moreover, if necessary, a symbol axis shift may additionally        occur. That is, although FIG. 6 shows only the frequency shift        according to each cell ID for the antenna port (1,2), it is also        possible to allocate the CSI-RSs to particular subcarriers of        (l=5 and 6) in cell group A and particular subcarriers of (l=2        and 3) in cell group B. The frequency shift may be different        according to the total number of antenna ports for all the        allocated CSI-RSs or according to the number of all reuse        factors required within one subframe. For example, if antenna        ports for 8 CSI-RSs are allocated, it is possible to generate a        total of three cell group-specific patterns, which are        discriminated from each other, within one subframe.    -   If 8, 4, and 2 CSI-RS antenna ports are used, it is possible to        generate 3, 6, and 12 discriminated cell group-specific patterns        (reuse factors having the orthogonality) within one subframe,        respectively, similarly to the preceding embodiments described        above. Further, the construction capable of muting or blanking        REs, to which CSI-RSs of another cell (cell group) are        allocated, is also the same as that in the preceding embodiments        described above.

The CSI-RSOCC allocation scheme according to the fifth embodiment of thepresent invention shown in FIG. 6 can be expressed by Equation 5 below.Equation 5 shows a representative example for helping the understandingof the present invention and may be expressed in another way within therange capable of maintaining the basic scheme described above.

-   -   CSI-RS antenna port=1, 3, 5, 7:OCC [+1,+1]    -   CSI-RS antenna port=2, 4, 6, 8:OCC [+1,−1]

$\begin{matrix}{{k = {{12 \cdot m} + {\left( {v + v_{shift}} \right){mod}\; 12}}}l = \left\{ {{{\begin{matrix}{5,6} & {{{{if}\mspace{14mu} {CSI}\text{-}{RS}\mspace{14mu} {antenna}\mspace{14mu} {port}} = 1},2,3,4} \\{2,3} & {{{{if}\mspace{14mu} {CSI}\text{-}{RS}\mspace{14mu} {antenna}\mspace{14mu} {port}} = 5},6,7,8}\end{matrix}m} = 0},1,2,\ldots \mspace{14mu},{{N_{RB}^{DL} - {1v}} = \left\{ {{\begin{matrix}2 & {{{{if}\mspace{14mu} {CSI}\text{-}{RS}\mspace{14mu} {antenna}\mspace{14mu} {port}} = 1},2,5,6} \\8 & {{{{if}\mspace{14mu} {CSI}\text{-}{RS}\mspace{14mu} {antenna}\mspace{14mu} {port}} = 3},4,7,8}\end{matrix}v_{shift}} = {N_{ID}^{cell}\; {mod}\mspace{11mu} 3}} \right.}} \right.} & \left\lbrack {{Equation}\mspace{14mu} 5} \right\rbrack\end{matrix}$

In the fifth embodiment of the present invention shown in FIG. 6, twopairs of consecutive symbol axes (l=2/3 and 5/6) are used, CSI-RSs ofantenna port Nos. (5, 6) and (1, 2) are allocated to locations where (l,k)=(2/3, 2) and (5/6, 2) and CSI-RSs of antenna port Nos. (7, 8) and (3,4) are allocated to locations where (l, k)=(2/3, 7) and (5/6, 7) in cellgroup A, and CSI-RSs are allocated in the same pattern to locations of(k=3, 8), which are frequency shifted by +1, in cell group B.

In this event, the number of antenna ports, in which the CSI-RS isduplicately allocated to the same RE, and the sequence of the numbers ofantenna ports in the frequency direction may change and are not limitedto the embodiment shown in FIG. 6.

Further, the combination and the sequence of the antenna port numbersallocated to corresponding positions may be changed and may be setaccording to each cell.

The fifth embodiment of the present invention as shown in FIG. 6 may bemodified into a configuration for two Physical Resource Blocks (PRBs) asshown in FIGS. 7 and 8, in order to perform a PRB-bundling for fullpower utilization.

That is, referring to FIGS. 7 and 8, four symbols are used within onePRB. In this event, if first two symbols are used for antenna ports ofantenna port Nos. 1, 2, 3, and 4 and the other two symbols are used forantenna ports of antenna port Nos. 5, 6, 7, and 8, CSI-RSs for antennaports of antenna port Nos. 5, 6, 7, and 8 are allocated, in thefollowing PRB (e.g. odd PRB), to the symbols, to which CSI-RSs forantenna ports of antenna port Nos. 1, 2, 3, and 4 have been allocated inthe previous PRB (e.g. even PRB). In contrast, CSI-RSs for antenna portsof antenna port Nos. 1, 2, 3, and 4 are allocated to the symbols, towhich CSI-RSs for antenna ports of antenna port Nos. 5, 6, 7, and 8 havebeen allocated in the previous PRB.

FIG. 9 shows a CSI-RS allocation scheme according to a sixth embodimentof the present invention, for a subframe in which the CP is a normal CP,the duplex scheme is TDD, and the number of OFDM symbols allocated tothe downlink (DwPTS) within the subframe is 9 or 10. However, in thesixth embodiment of the present invention, duplicated allocation of AP5is not allowed, differently from the fifth embodiment of the presentinvention.

In this event, the subframe is the special subframe as described above.

In the sixth embodiment of the present invention, whether to use AP2 orAP3 is not considered.

The following configuration is applied to the sixth embodiment of thepresent invention shown in FIG. 9.

-   -   Two consecutive OFDM symbols are used, and the CSI-RSs may be        allocated to two different consecutive symbol axes according to        the cell (or cell group).    -   It is the same as in the first embodiment of the present        invention shown in FIG. 2 in view of that an antenna port is        identified by an OCC code and the CSI-RSs are allocated to REs        corresponding to one half of the number of antenna ports for        each symbol in the second embodiment of the present invention.    -   CSI-RSs may be configured for a total of two basic cell groups        discriminated from each other. In the first cell group, CSI-RSs        are allocated to the 6th and 7th symbol axes (l=5, 6) and to the        other REs except for the REs, at which AP5 and Rel-9/10 DM-RS        are located, in the 6th and 7th symbol axes (l=5, 6). In the        second cell group, CSI-RSs are allocated to the 3rd and 4th        symbol axes (l=2, 3) and to the other REs except for the REs, at        which AP5 and Rel-9/10 DM-RS are located, in the 3rd and 4th        symbol axes (l=3, 4).    -   If 8 CSI-RS antenna ports are used, it is possible to generate        two discriminated cell group-specific patterns (reuse factors        having the orthogonality) within one subframe. Further, if 2 or        4 CSI-RS antenna ports are used, it is possible to generate a        maximum of 8 or 4 discriminated cell group-specific patterns        (reuse factors having the orthogonality) within one subframe. To        this end, each cell group-specific CSI-RS pattern is shifted in        the frequency and symbol axes. For example, antenna port (1, 2)        is allocated to (l, k)=(5/6, 3) in cell group A while it is        allocated to (l, k)=(2/3, 2) in cell group B, which corresponds        to a shift of −3 in the frequency axis and a shift of −1 in the        symbol axis between the cell groups.

That is, the number of all REs configured in order to generate eachcell-specific pattern is a maximum of 16 (or two times of the number ofantenna ports for allocated CSI-RSs) within one subframe, and the mutingor blanking as described above may be applied.

The CSI-RS allocation scheme according to the sixth embodiment of thepresent invention shown in FIG. 9 can be expressed by Equation 6 below.Equation 6 shows a representative example for helping the understandingof the present invention and may be expressed in another way within therange capable of maintaining the basic scheme described above.

-   -   CSI-RS antenna port=1, 3, 5, 7:OCC [+1,+1]    -   CSI-RS antenna port=2, 4, 6, 8:OCC [+1,−1]

$\begin{matrix}{{k = {{12 \cdot m} + {\left( {v + v_{shift}} \right){mod}\; 12}}}{l = \left\{ {{{\begin{matrix}{5,6} & {{{if}\mspace{14mu} N_{ID}^{cell}{mod}\mspace{11mu} 2} = 0} \\{2,3} & {{{if}\mspace{14mu} N_{ID}^{cell}{mod}\mspace{11mu} 2} = 1}\end{matrix}m} = 0},1,2,\ldots \mspace{14mu},{{N_{RB}^{DL} - {1v}} = \left\{ {{\begin{matrix}3 & {{{{if}\mspace{14mu} {CSI}\text{-}{RS}\mspace{14mu} {antenna}\mspace{14mu} {port}} = 1},2} \\7 & {{{{if}\mspace{14mu} {CSI}\text{-}{RS}\mspace{14mu} {antenna}\mspace{14mu} {port}} = 3},4} \\4 & {{{{if}\mspace{14mu} {CSI}\text{-}{RS}\mspace{14mu} {antenna}\mspace{14mu} {port}} = 5},6} \\9 & {{{{if}\mspace{14mu} {CSI}\text{-}{RS}\mspace{14mu} {antenna}\mspace{14mu} {port}} = 7},8}\end{matrix}v_{shift}} = \left\{ \begin{matrix}{- 1} & \begin{matrix}{{{if}\mspace{14mu} N_{ID}^{cell}{mod}{\; \;}2} = {1\mspace{14mu} {and}}} \\{{{{CSI}\text{-}{RS}\mspace{14mu} {antenna}\mspace{14mu} {port}} = 1},2,5,6}\end{matrix} \\0 & {else}\end{matrix} \right.} \right.}} \right.}} & \left\lbrack {{Equation}\mspace{14mu} 6} \right\rbrack\end{matrix}$

In conclusion, according to the sixth embodiment shown in FIG. 9, twoconsecutive cell group-specific symbol axes (l=5/6, 2/3) are used,wherein one cell group A may be shifted by +1 from the other cell groupsB and C in the frequency axis.

Further, the combination and the sequence of the antenna port numbersallocated to corresponding positions may be changed and may be setaccording to each cell. Although FIG. 9 shows a scheme of allocating acombination of (1,2)+(5,6) to four neighbor REs while allocating (3,4)and (7,8) to spaced REs, the present invention is not limited to thescheme shown in FIG. 9 and may employ another combination or sequence.

FIG. 10 shows a CSI-RS allocation scheme according to a seventhembodiment of the present invention, for a downlink subframe in whichthe CP is an extended CP, the duplex scheme is FDD or TDD, and aduplicated allocation of AP5 is allowed (that is, CSI-RS allocation tothe location of AP5 is allowed).

However, in the seventh embodiment of the present invention, the case inwhich AP2 or AP3 is not used is taken into account, which may differfrom the preceding embodiments described above.

The following configuration is applied to the seventh embodiment of thepresent invention shown in FIG. 10.

-   -   Two consecutive OFDM symbols are used, which may include the 8th        and the 9th symbols (i.e. l=7 and 8).    -   Every two antenna ports are tied into one pair, and the pairs        are multiplexed by FDM while two consecutive OFDM symbols for        two antenna ports within each pair are multiplexed by CDM (i.e.        CDM-T) by using an orthogonal code such as the Orthogonal Cove        Code (OCC), as in the embodiments described above.    -   Antenna ports for 2/4/8 CSI-RSs may be allocated to two symbols        (if 3/5/7 antenna ports are allocated, addition of one more        antenna port to the corresponding number of antenna ports is        considered. That is, if 7 antenna ports are allocated, 8 antenna        ports are considered for the CSI-RS configuration, which results        in that the number of antenna ports is 8 and one half of the        number of antenna ports being 4), and the CSI-RSs are allocated        to REs corresponding to one half of the number of antenna ports        for each symbol. For example, if antenna ports for 8 CSI-RSs are        allocated, CSI-RSs for each antenna port are allocated to 4 REs        (or subcarriers) in each symbol.    -   An interval of REs corresponding to “24/(number of antenna        ports)” along the frequency axis is arranged between neighbor        CSI-RS allocated REs for one symbol axis. For example, if        antenna ports for 8 CSI-RSs are allocated, an interval of 3 REs        along the frequency axis is established (which implies that 2        empty REs exist) between neighbor CSI-RS allocated REs for one        symbol axis.    -   According to the cell group ID, a frequency shift may occur by        the unit of a total of 12 subcarriers. In this event, based on        the interval between neighbor CSI-RS allocated REs, it is        possible to generate cell group-specific patterns (reuse factor        having the orthogonality), which are discriminated from each        other and correspond to a maximum of “24/(number of antenna        ports)”, within one subframe. In this event, for example, if        antenna ports for 8 CSI-RSs are allocated, it is possible to        generate a total of three cell group-specific patterns, which        are discriminated from each other, within one subframe.

Among the REs, it is possible to perform the blanking, which empties theREs, to which another cell group except for its own cell group (the cellgroup to which the serving cell belongs) sends CSI-RSs, without sendingdata to the REs, or the muting, which performs the transmission usingzero power.

The CSI-RS allocation scheme according to the seventh embodiment of thepresent invention shown in FIG. 10 as described above can be expressedby Equation 7 below. Equation 7 shows a representative example forhelping the understanding of the present invention and may be expressedin another way within the range capable of maintaining the basic schemedescribed above.

-   -   CSI-RS antenna port=1, 3, 5, 7:OCC [+1,+1]    -   CSI-RS antenna port=2, 4, 6, 8:OCC [+1,−1]

$\begin{matrix}{{k = {{12 \cdot m} + {\left( {v + v_{shift}} \right){mod}\; 12}}}{{l = 7},8}{{m = 0},1,2,\ldots \mspace{14mu},{N_{RB}^{DL} - 1}}{v = \left\{ {{\begin{matrix}0 & {{{{if}\mspace{14mu} {CSI}\text{-}{RS}\mspace{14mu} {antenna}\mspace{14mu} {port}} = 1},2} \\6 & {{{{if}\mspace{14mu} {CSI}\text{-}{RS}\mspace{14mu} {antenna}\mspace{14mu} {port}} = 3},4} \\3 & {{{{if}\mspace{14mu} {CSI}\text{-}{RS}\mspace{14mu} {antenna}\mspace{14mu} {port}} = 5},6} \\9 & {{{{if}\mspace{14mu} {CSI}\text{-}{RS}\mspace{14mu} {antenna}\mspace{14mu} {port}} = 7},8}\end{matrix}v_{shift}} = {N_{ID}^{cell}\; {mod}\; 12}} \right.}} & \left\lbrack {{Equation}\mspace{14mu} 7} \right\rbrack\end{matrix}$

In Equation 7, k indicates a subcarrier number, l indicates a symbolnumber, N_(ID) ^(cell) indicates a cell ID, and N_(RB) ^(DL) indicatesthe number of downlink RBs.

As described above, in the seventh embodiment of the present inventionas shown in FIG. 10, CSI-RSs of antenna ports number (1,2), (5,6),(3,4), and (7,8) for CSI-RS are allocated to the locations where k=0, 3,6, and 9, respectively, in the symbol axes of (l=7 and 8) in cell groupA, CSI-RSs of antenna ports number (1,2), (5,6), (3,4), and (7,8) forCSI-RS are allocated to the locations where k=1, 4, 7, and 10,respectively, which are shifted by +1 along the frequency axis, in thesame symbol axis in cell group B, and CSI-RSs of antenna ports number(1,2), (5,6), (3,4), and (7,8) for CSI-RS are allocated to the locationswhere k=2, 5, 8, and 10, respectively, in cell group C.

In this event, the number of the antenna port, in which the CSI-RS isduplicately allocated to the same RE, and the sequence of the numbers ofantenna ports in the frequency direction may change and are not limitedby the embodiment shown in FIG. 10. That is, in FIG. 10, as the index ofthe subcarrier increases, the allocation is performed in the sequence of(1,2), (5,6), (3,4), and (7,8). However, this is not a requirement andanother antenna port combination or another sequence, such as the orderof the antenna port number (1,2), (3,4), (5,6), and (7,8), may beemployed for the allocation, if the index of the subcarrier increases ordecreases. In other words, CSI-RSs of a higher antenna port number maybe allocated to an RE having a lower subcarrier index. For example,CSI-RSs of the 7th and 8th antenna ports (antenna port Nos. 6 and 7) maybe allocated to two REs having a subcarrier index within a RB of 0 (1stsubcarrier), and CSI-RSs of the (5th, 6th), (3rd, 4th), (1st, 2nd)antenna ports (i.e. antenna port Nos. are (4, 5), (2, 3), and (0, 1),respectively) may be allocated to two REs having subcarrier indexeswithin a RB of 3, 6, and 9 (i.e. 4th, 7th and 10th subcarriers,respectively), respectively.

However, as shown in FIG. 10, antenna ports duplicately allocated to oneRE may be neighbor antenna ports adjacent to each other. That is, inFIG. 10, the antenna ports duplicately allocated to (l, k)=(7/8, 0) maybe antenna port 1 and antenna port 2, which are adjacent to each other.

However, the combination and the sequence of the antenna port numbersarranged in the frequency direction are not necessarily limited to FIG.10, and another combination or sequence may be employed.

FIG. 11 shows a CSI-RS allocation scheme according to an eighthembodiment of the present invention, for a subframe in which the CP isan extended CP, the duplex scheme is TDD, the number of OFDM symbols forthe downlink (DwPTS) within the subframe is 8 or 9/10, and a duplicatedallocation of AP5 is allowed (that is, CSI-RS allocation to the locationof AP5 is allowed).

Further, as in the seventh embodiment of the present invention, only thecase in which AP2 or AP3 is not used is taken into account.

In this event, the subframe mentioned above corresponds to the specialsubframe.

The following configuration is applied to the eighth embodiment of thepresent invention shown in FIG. 11.

-   -   Two consecutive OFDM symbols are used. For example, the        consecutive 8th and 9th OFDM symbol axes (l=7, 8) may be used if        the number of OFDM symbols for the downlink (DwPTS) in the        special subframe is 9 or 10, and the 3rd and 8th OFDM symbol        axes (l=2, 7) may be used if the number of OFDM symbols for the        downlink (DwPTS) in the special subframe is 8.    -   It is the same as in the preceding embodiments of the present        invention described above in view of that an antenna port is        identified by an OCC code and the CSI-RSs are allocated to REs        corresponding to one half of the number of antenna ports for        each symbol.    -   As in the preceding embodiments of the present invention        described above, an interval of REs corresponding to “24/(number        of antenna ports)” along the frequency axis is arranged between        neighbor CSI-RSs allocated REs for one symbol axis. Also,        according to the cell group ID, it is possible to generate cell        group-specific patterns, which are discriminated from each other        and correspond to a maximum of “24/(number of antenna ports)”,        within one subframe. Further, the construction capable of muting        or blanking REs, to which CSI-RSs of another cell (or cell        group) are allocated, is also similar to that in the preceding        embodiments of the present invention.

The CSI-RS allocation scheme according to the eighth embodiment of thepresent invention shown in FIG. 11 can be expressed by Equation 8 below.Equation 8 shows a representative example for helping the understandingof the present invention and may be expressed in another way within therange capable of maintaining the basic scheme described above.

-   -   CSI-RS antenna port=1, 3, 5, 7:OCC [+1,+1]    -   CSI-RS antenna port=2, 4, 6, 8:OCC [+1,−1]

$\begin{matrix}{\mspace{79mu} {{k = {{12 \cdot m} + {\left( {v + v_{shift}} \right){mod}\; 12}}}{l = \left\{ {{{\begin{matrix}{7,8} & {{{if}\mspace{14mu} {in}\mspace{14mu} a\mspace{14mu} {special}\mspace{14mu} {subframe}\mspace{14mu} {with}\mspace{14mu} 9},{10\mspace{14mu} {OFDM}\mspace{14mu} {symols}}} \\{2,7} & {{if}\mspace{14mu} {in}\mspace{14mu} a\mspace{14mu} {special}\mspace{14mu} {subframe}\mspace{14mu} {with}\mspace{14mu} 8\mspace{14mu} {OFDM}\mspace{14mu} {symols}}\end{matrix}\mspace{79mu} m} = 0},1,2,\ldots \mspace{14mu},{{N_{RB}^{DL} - {1\mspace{79mu} v}} = \left\{ {{\begin{matrix}0 & {{{{if}\mspace{14mu} {CSI}\text{-}{RS}\mspace{14mu} {antenna}\mspace{14mu} {port}} = 1},2} \\6 & {{{{if}\mspace{14mu} {CSI}\text{-}{RS}\mspace{14mu} {antenna}\mspace{14mu} {port}} = 3},4} \\3 & {{{{if}\mspace{14mu} {CSI}\text{-}{RS}\mspace{14mu} {antenna}\mspace{14mu} {port}} = 5},6} \\9 & {{{{if}\mspace{14mu} {CSI}\text{-}{RS}\mspace{14mu} {antenna}\mspace{14mu} {port}} = 7},8}\end{matrix}\mspace{79mu} v_{shift}} = {N_{ID}^{cell}\; {mod}\; 12}} \right.}} \right.}}} & \left\lbrack {{Equation}\mspace{14mu} 8} \right\rbrack\end{matrix}$

In the eighth embodiment of the present invention described above, ifthe number (DwPTS) of OFDM symbols used for the downlink within onesubframe is 9 or 10, as shown in FIG. 11, CSI-RSs of (1,2), (5,6),(3,4), and (7,8) are allocated to the locations where k=0, 3, 6, and 9,respectively, in the symbol axes of (l=9 and 10) in cell group A,CSI-RSs of (1,2), (5,6), (3,4), and (7,8) are allocated to the locationswhere k=1, 4, 7, and 10, respectively, which are shifted by +1 along thefrequency axis, in the same symbol axis in cell group B, and CSI-RSs of(1,2), (5,6), (3,4), and (7,8) are allocated to the locations where k=2,5, 8, and 10, respectively, in cell group C.

In this event, the number of the antenna port, in which the CSI-RS isduplicately allocated to the same RE, and the sequence of the numbers ofantenna ports in the frequency direction may change, and antenna portsduplicately allocated to a single RE are antenna ports adjacent to eachother, as in the preceding embodiments described above.

In the first to eighth embodiments of the present invention, the numberof reuse factors for one subframe, that is, the number of orthogonalpatterns, which are discriminated according to cell groups, is 2 or 3,and is 3 in most cases.

In the case of using a subframe shift or an offset, the total reusefactor corresponds to “a reuse factor within one subframe x the numberof subframes allocatable within one CSI-RS cycle”. For example, if thereuse factor within one subframe is 3, the transmission cycle is 5 ms,and the number of allocatable subframes is 4 except for the subframe, towhich the primary synchronization signal (PSS) and the secondarysynchronization signal (SSS) are allocated, and the total reuse factormay be 12 (3*4=12).

FIGS. 12, 13, and 14 illustrate CSI-RS allocation schemes additionallytaking a frequency shift (v-shift) of AP5 into consideration to theembodiments shown in FIGS. 3, 5, and 9.

As described above, FIG. 3 shows a CSI-RS allocation scheme according toa second embodiment of the present invention, for a downlink subframe inwhich the CP is a normal CP and the duplex scheme is FDD or TDD.Further, in the CSI-RS allocation scheme shown in FIG. 3, a duplicatedallocation of AP5 is not allowed, and whether to use AP2 or AP3 is notconsidered. Moreover, the mapping scheme in FIG. 3 does not take thefrequency shift of AP5 into consideration, that is, corresponds to ascheme if v-shift=0. If the frequency shift of AP5 is taken intoconsideration, for example, if the v-shift=1 or 2, the CSI-RS allocationscheme according to a second embodiment of the present invention shownin FIG. 3 can be modified to that shown in FIG. 12.

The following configuration is applied to the CSI-RS allocation schemeshown in FIG. 12.

-   -   The CSI-RS allocation scheme without consideration of the        v-shift is similar to the second embodiment shown in FIG. 3, so        a detailed description thereof is omitted here.    -   Besides the three discriminated basic cell groups, three bundles        of cell groups in relation to the frequency shift of AP5 may        also be used. The three bundles of cell groups correspond to        cases where v-shift=0, v-shift=1, and v-shift=2, respectively.        For each of the v-shifts, three basic cell groups are        correlated. For example, if the total cell groups include 9        groups, each bundle including three basic cell groups is related        to the v-shift, and there are a total of three bundles of cell        groups, each including three basic cell groups relating to the        v-shifts, in relation to a total of three AP5 s.    -   It may be possible to simply divide the total cell groups into        three bundles of cell groups and then define just a single cell        group within a bundle of three cell groups relating to the        v-shift. That is, in FIG. 12, it is possible to select only one        cell group from the three cell groups included in each of the        cell group bundles 1, 2, and 3 relating to the v-shift.

As in the embodiments described above, when 8, 4, and 2 CSI-RS antennaports are used, it is possible to generate 3, 6, and 9 perfectlydiscriminated cell group-specific patterns (reuse factors having theorthogonality) within one subframe, respectively. Further, theconstruction capable of muting or blanking REs, to which CSI-RSs ofanother cell (cell group) are allocated, is also the same as that in thefirst embodiment shown in FIG. 2. Moreover, the change in the number ofantenna port, in which the CSI-RS is duplicately allocated to the sameRE, and the sequence of the numbers of antenna ports in the frequencydirection may be similar to that of the embodiments described above.

FIG. 13 illustrates a CSI-RS allocation scheme additionally taking afrequency shift (v-shift=0, 1, or 2) of AP5 into consideration to thefourth embodiment shown in FIG. 5.

The following configuration is applied to the CSI-RS allocation schemeshown in FIG. 13.

-   -   The basic configuration of the CSI-RS allocation scheme shown in        FIG. 13 is similar to the fourth embodiment shown in FIG. 5, so        a detailed description thereof is omitted here.

However, the embodiment shown in FIG. 13 is different from the fourthembodiment in that the CSI-RS allocation pattern corresponding to thesecond cell group is generated by shifting the CSI-RS allocation patterncorresponding to the first cell group by −3 in the OFDM symbol axiscorresponding to time and by +2 in the subcarrier axis corresponding tofrequency in the embodiment shown in FIG. 13 (however, the CSI-RSallocation pattern corresponding to the second cell group is generatedby shifting the CSI-RS allocation pattern corresponding to the firstcell group by −3 in the OFDM symbol axis corresponding to time and by −2in the subcarrier axis corresponding to frequency the fourthembodiment).

-   -   Besides the three discriminated basic cell groups, three bundles        of cell groups in relation to the frequency shift of AP5 may be        used. As in the structure shown in FIG. 12, each of the three        bundles of cell groups, each of which includes three basic cell        groups among the total 9 cell groups, is related to the v-shift        while preventing overlapping between the bundles.

Further, although FIG. 13 shows a scheme of allocating a combination of(1,2)+(5,6) to four neighbor REs while allocating (3,4) and (7,8) tospaced REs, the present invention is not limited to the scheme shown inFIG. 5 and may employ another combination or sequence.

FIG. 14 corresponds to the sixth embodiment of the present inventionshown in FIG. 9 and illustrates a CSI-RS allocation scheme additionallytaking a frequency shift (v-shift=0, 1, or 2) of AP5 into consideration.

-   -   The basic configuration of the CSI-RS allocation scheme shown in        FIG. 14 is similar to the sixth embodiment shown in FIG. 9, so a        detailed description thereof is omitted here.

However, in the embodiment shown in FIG. 13, besides the twodiscriminated basic cell groups shown in FIG. 9, three bundles of cellgroups in relation to the frequency shift of AP5 may be used. The threebundles of cell groups correspond to the cases where v-shift=0,v-shift=1, and v-shift=2, respectively. For each of the v-shifts, twobasic cell groups are correlated, as described above. For example, ifthe total cell groups are divided into 6 groups, each bundle includingtwo basic cell groups is related to the v-shift, and there are a totalof three bundles of cell groups, each including two basic cell groupsrelating to the v-shifts, in relation to a total of three AP5s.

-   -   It may be possible to simply divide the total cell groups into        two bundles of cell groups and then define just a single cell        group within each bundle of three cell groups relating to the        v-shift. That is, in FIG. 14, it is possible to select only one        cell group from the two cell groups included in each of the cell        group bundles 1 and 2 relating to the v-shift.

Further, the number of the antenna port, in which the CSI-RS isduplicately allocated to the same RE, and the sequence of the numbers ofantenna ports in the frequency direction may change according to thecells. In addition, although FIG. 14 shows a scheme of allocating acombination of (1,2)+(5,6) to four neighbor REs while allocating (3,4)and (7,8) to spaced REs, in a manner slightly different from that ofFIG. 9, the present invention is not limited to the scheme shown in FIG.5 and may employ another combination or sequence.

According to the embodiments of the present invention, it is possible toallocate CSI-RSs to resource areas, so as to enable each cell to havethe orthogonality, according to whether it is possible to duplicatelyallocate a CSI-RS to antenna No. 5 (AP5) and in consideration of thesubframe structure information including the CP length, Duplex scheme,and the number of symbols allocated to the downlink (DwPTS) in the caseof TDD. Therefore, it is possible to transmit the CSI-RSs of antennaports for multiple cells (cell groups) without interference.

FIG. 15 is a block diagram illustrating a receiving apparatus forreceiving CSI-RSs transmitted according to a CSI-RS allocation andtransmission scheme according to an exemplary embodiment of the presentinvention.

Referring to FIG. 15, the receiving apparatus 1500 of a UE in a wirelesscommunication system includes a signal receiver 1510, a CSI-RS extractor1520 which can be included a RE demapper, a CSI-RS sequence decoder1530, and a channel state measurer 1540.

The signal receiver 1510 receives a signal through each antenna port ofthe receiving apparatus 1500, and the CSI-RS extractor 1520 extractsonly the CSI-RSs for each of the multiple antenna ports allocated toparticular REs from the received signal.

The CSI-RS sequence decoder 1530 decodes a CSI-RS sequence for eachantenna port. The CSI-RS extractor 1520 and/or the CSI-RS sequencedecoder may follow an inverse order to the CSI-RS allocation schemeaccording to one of the schemes described above with reference to FIGS.2 to 14, and the channel state measurer 1540 acquires Channel SpatialInformation (CSI), which is channel state information for each antennaport in a multiple antenna system including multiple antennas, throughthe de-mapped CSI-RSs.

FIG. 16 is a flowchart illustrating a method of allocating CSI-RSsaccording to an embodiment of the present invention.

The method of allocating CSI-RSs according to an embodiment of thepresent invention includes the steps of: generating a CSI-RS for eachcell (or cell group) and for each antenna port (step S1610); identifyingsubframe configuration information of a subframe allocated the CSI-RSsand system information including cell (or cell group) identificationinformation (step S1620); and allocating CSI-RS of each antenna port toa resource area while enabling one or more cells (or cell groups) tohave an orthogonality in the frequency/time resource by using thesubframe configuration information and the system information (stepS1630).

The subframe configuration information may include the CP length, theduplex scheme, and the number of OFDM symbols for the downlink (DwPTS)within a special subframe if the duplex scheme is TDD, and may furtherinclude information on whether to perform duplicated allocation of AP5(i.e. whether to duplicately allocate CSI-RSs to a location at which theCRS of AP5 is allocated) in the allocation step.

In the step of allocating the CSI-RS (step S1630), the CSI-RSs of eachcell (cell group) and for each antenna port are allocated to thetime/frequency resource area according to the schemes described abovewith reference to FIGS. 2 to 14, in consideration of the subframe typedetermined by the identified subframe configuration information(including the CP length & duplex scheme) and existence or absence ofduplicated resource allocation of AP5.

In this event, especially under the condition of a subframe as in theembodiment shown in FIG. 10, in which the CP is an extended CP, theduplex scheme is TDD, and a duplicated allocation to AP5 is allowed, ifCSI-RSs for maximum 8 antenna ports are allocated, the CSI-RSs may beallocated to the 8th and 9th symbols (symbol number l=7 and 8), in sucha manner that each CSI-RS for every two antenna ports is allocated tothe same RE while being discriminated from each other by an orthogonalcode and neighbor CSI-RSs allocated REs in the frequency axis are spacedby an interval of three REs.

The CSI-RS allocation schemes according to embodiments of the presentinvention as described above with reference to FIGS. 2 to 11 may be usedunder various conditions, a detailed description of which is omittedhere in order to avoid repetition of description.

By using the embodiments described above, it may be possible to allocateCSI-RSs to a time-frequency resource area with securing a orthogonalitybetween cells (cell groups) for each of various types of subframes whilemaintaining the CSI-RS transmission overhead. As a result, it may bepossible to reduce the performance degradation due to interferencebetween neighbor cells.

The embodiments of the present invention as described above provide anapparatus and a method for allocating CSI-RSs to resource areas, so asto enable cells to have the orthogonality, according to whether it ispossible to duplicately allocate a CSI-RS to antenna No. 5 (AP5) and inconsideration of the subframe structure information including the CPlength, Duplex scheme, and the number of symbols allocated to thedownlink (DwPTS) within a special subframe in the case of TDD. As aresult, it is possible to reduce the performance degradation due tointerference between neighbor cells in various types of subframestructures.

While the exemplary embodiments have been shown and described, it willbe understood by those skilled in the art that various changes in formand details may be made thereto without departing from the spirit andscope of this disclosure as defined by the appended claims and theirequivalents. Thus, as long as modifications fall within the scope of theappended claims and their equivalents, they should not be misconstruedas a departure from the scope of the invention itself.

What is claimed is:
 1. A method, comprising: allocating, by a basestation (BS), Channel State Information Reference Signals (CSI-RSs) forfour pairs of antenna ports to a portion of Resource Elements (REs) in atime-frequency resource area determined by one subframe and 12subcarriers, wherein two CSI-RSs in one of the four pairs of antennaports are associated with different orthogonal codes, respectively,wherein the CSI-RSs of a first pair (1st, 2nd) of antenna ports areallocated to a first two consecutive REs, the CSI-RSs of a second pair(3rd, 4th) of antenna ports are allocated to a second two consecutiveREs, the CSI-RSs of a third pair (5th, 6th) of antenna ports areallocated to a third two consecutive REs, and the CSI-RSs of a fourthpair (7th, 8th) of antenna ports are allocated to a fourth twoconsecutive REs, wherein each of the first two consecutive REs, thesecond two consecutive REs, the third two consecutive REs, and thefourth two consecutive REs corresponds to one subcarrier in a frequencyaxis and 8th and 9th symbols in a time axis, and wherein the first twoconsecutive REs has subcarrier index 9, the second two consecutive REshas subcarrier index 6, the third two consecutive REs has subcarrierindex 3, and the fourth two consecutive REs has subcarrier index
 0. 2.The method of claim 1, wherein the (7th, 8th) antenna ports have higherantenna port numbers than antenna port numbers of the (5th, 6th) antennaports, wherein the (5th, 6th) antenna ports have higher antenna portnumbers than antenna port numbers of the (3rd, 4th) antenna ports, andwherein the (3rd, 4th) antenna ports have higher antenna port numbersthan antenna port numbers of the (1st, 2nd) antenna ports.
 3. The methodof claim 1, wherein the two antenna ports in each of the four pairs ofantenna ports have consecutive antenna port numbers.
 4. The method ofclaim 1, wherein the different orthogonal codes include a firstorthogonal cover code (OCC) and a second OCC, and wherein the first OCChas a value of 1 mapped to the 8th symbol and a value of 1 mapped to the9th symbol, and the second OCC has a value of 1 mapped to the 8th symboland a value of −1 mapped to the 9th symbol.
 5. The method of claim 1,wherein the two CSI-RSs in one of the four pairs of antenna ports areconfigured to be discriminated from each other by the differentorthogonal codes.
 6. The method of claim 1, wherein the one subframe has12 symbols for an extended Cyclic Prefix (CP).
 7. A method, comprising:receiving and extracting, by a User Equipment (UE), Channel StateInformation Reference Signals (CSI-RSs) for four pairs of antenna portsbeing allocated to a portion of Resource Elements (REs) in atime-frequency resource area determined by one subframe and 12subcarriers; and acquiring Channel State Information (CSI) based on theextracted CSI-RSs, wherein two CSI-RSs in one of the four pairs ofantenna ports are associated with different orthogonal codes,respectively, wherein the CSI-RSs of a first pair (1st, 2nd) of antennaports are allocated to a first two consecutive REs, the CSI-RSs of asecond pair (3rd, 4th) of antenna ports are allocated to a second twoconsecutive REs, the CSI-RSs of a third pair (5th, 6th) of antenna portsare allocated to a third two consecutive REs, and the CSI-RSs of afourth pair (7th, 8th) of antenna ports are allocated to a fourth twoconsecutive REs, wherein each of the first two consecutive REs, thesecond two consecutive REs, the third two consecutive REs, and thefourth two consecutive REs corresponds to one subcarrier in a frequencyaxis and 8th and 9th symbols in a time axis, and wherein the first twoconsecutive REs has subcarrier index 9, the second two consecutive REshas subcarrier index 6, the third two consecutive REs has subcarrierindex 3, and the fourth two consecutive REs has subcarrier index
 0. 8.The method of claim 7, wherein the (7th, 8th) antenna ports have higherantenna port numbers than antenna port numbers of the (5th, 6th) antennaports, wherein the (5th, 6th) antenna ports have higher antenna portnumbers than antenna port numbers of the (3rd, 4th) antenna ports, andwherein the (3rd, 4th) antenna ports have higher antenna port numbersthan antenna port numbers of the (1st, 2nd) antenna ports.
 9. The methodof claim 7, wherein the two antenna ports in each of the four pairs ofantenna ports have consecutive antenna port numbers.
 10. The method ofclaim 7, wherein the different orthogonal codes include a firstorthogonal cover code (OCC) and a second OCC, and wherein the first OCChas a value of 1 mapped to the 8th symbol and a value of 1 mapped to the9th symbol, and the second OCC has a value of 1 mapped to the 8th symboland a value of −1 mapped to the 9th symbol.
 11. The method of claim 7,wherein the two CSI-RSs in one of the four pairs of antenna ports areconfigured to be discriminated from each other by the differentorthogonal codes.
 12. The method of claim 7, wherein the one subframehas 12 symbols for an extended Cyclic Prefix (CP).
 13. An apparatus,comprising: a processor configured to allocate Channel StateInformation-Reference Signals (CSI-RSs) for four pairs of antenna portsin a wireless communication system, wherein the CSI-RSs of the fourpairs of antenna ports are allocated to a portion of Resource Elements(REs) in a time-frequency resource area determined by one subframe and12 subcarriers, wherein two CSI-RSs in one of the four pairs of antennaports are associated with different orthogonal codes, respectively,wherein the CSI-RSs of a first pair (1st, 2nd) of antenna ports areallocated to a first two consecutive REs, the CSI-RSs of a second pair(3rd, 4th) of antenna ports are allocated to a second two consecutiveREs, the CSI-RSs of a third pair (5th, 6th) of antenna ports areallocated to a third two consecutive REs, and the CSI-RSs of a fourthpair (7th, 8th) of antenna ports are allocated to a fourth twoconsecutive REs, wherein each of the first two consecutive REs, thesecond two consecutive REs, the third two consecutive REs, and thefourth two consecutive REs corresponds to one subcarrier in a frequencyaxis and 8th and 9th symbols in a time axis, and wherein the first twoconsecutive REs has subcarrier index 9, the second two consecutive REshas subcarrier index 6, the third two consecutive REs has subcarrierindex 3, and the fourth two consecutive REs has subcarrier index
 0. 14.The apparatus of claim 13, wherein the (7th, 8th) antenna ports havehigher antenna port numbers than antenna port numbers of the (5th, 6th)antenna ports, wherein the (5th, 6th) antenna ports have higher antennaport numbers than antenna port numbers of the (3rd, 4th) antenna ports,and wherein the (3rd, 4th) antenna ports have higher antenna portnumbers than antenna port numbers of the (1st, 2nd) antenna ports. 15.The apparatus of claim 13, wherein the two antenna ports in each of thefour pairs of antenna ports have consecutive antenna port numbers. 16.The apparatus of claim 13, wherein the different orthogonal codesinclude a first orthogonal cover code (OCC) and a second OCC, andwherein the first OCC has a value of 1 mapped to the 8th symbol and avalue of 1 mapped to the 9th symbol, and the second OCC has a value of 1mapped to the 8th symbol and a value of −1 mapped to the 9th symbol. 17.The apparatus of claim 13, wherein the two CSI-RSs in one of the fourpairs of antenna ports are configured to be discriminated from eachother by the different orthogonal codes.
 18. The apparatus of claim 13,wherein the one subframe has 12 symbols for an extended Cyclic Prefix(CP).